1. Field of the Invention
The subject invention is generally related to digital cameras and sensors and is specifically directed to a multimedia sensor of use in connection with a digital networked surveillance system. The subject invention in it's preferred embodiment is a networked appliance.
2. Discussion of the Prior Art
Security of public facilities such as schools, banks, airports, arenas and the like is a topic of increasing concern in recent years. Over the past few years, a number of violent incidents including bombings, shootings, arson, and hostage situations have occurred. In addition, agencies responsible for public security in these facilities must cope with more commonplace crimes, such as drug dealing, vandalism, theft and the like.
Such facilities frequently employ monitoring and surveillance systems to enhance security. This has been common practice for a number of years. Such systems generally have a centralized monitoring console, usually attended by a guard or dispatcher. A variety of sensors are located throughout the facility, such as smoke detectors, fire detectors, motion sensors, glass breakage detectors, badge readers at various access points, and sometimes, video cameras and/or microphones. These prior-art systems often use technologies that are somewhat dated. Sensors are not ‘intelligent’ in the modern sense; they merely provide an ‘ON/OFF’ indication to the centralized monitoring system. The sensors are not ‘networked’ in the modern sense; they are generally hard-wired to the centralized monitoring system via a ‘current loop’ or similar arrangement, and do not provide situational data other than their ON/OFF status.
Video systems in common use today are particularly dated—they are generally of low quality, using analog signals conveyed over coaxial or, occasionally, twisted-pair cabling to the centralized monitoring facility. Such visual information is generally archived on analog video recorders. Further, such systems generally do not have the ability to ‘share’ the captured video, and such video is generally viewable only on the system's control console.
Prior art systems have typically employed analog cameras, using composite video at frame rates up to the standard 30 frames/second. Many such systems have been monochrome systems, which are less costly and provide marginally better resolution with slightly greater sensitivity under poor lighting conditions than current analog color systems. Traditional video cameras have used CCD or CMOS area sensors to capture the desired image. The resolution of such cameras is generally limited to the standard CCTV 300–350 lines of resolution, and the standard 480 active scan lines.
Such cameras are deployed around the area to be observed, and are connected to a centralized monitoring/recording system via coaxial cable or, less often, twisted-pair (UTP) wiring. The signals conveyed over such wiring are almost universally analog, composite video. Baseband video signals are generally employed, although some such systems modulate the video signals on to an RF carrier, using either AM or FM techniques. In each case, the video is subject to degradation due to the usual causes—crosstalk in the wiring plant, AC ground noise, interfering carriers, and so on.
More recently, security cameras have employed video compression technology, enabling the individual cameras to be connected to the centralized system via telephone circuits. Due to the bandwidth constraints imposed by the public-switched telephone system, such systems are typically limited to low-resolution images, or to low frame rates, or both.
Prior-art surveillance systems were oriented towards delivering a captured video signal to a centralized monitoring facility or console. In the case of analog composite video signals, these signals were transported as analog signals over coaxial cable or twisted-pair wiring, to the monitoring facility. In other systems, the video signals were compressed down to very low bit rates, suitable for transmission over the public-switched telephone network.
Each of these prior-art systems suffers functional disadvantages. The composite video/coaxial cable approach provides full-motion video but can only convey it to a local monitoring facility. The low-bit rate approach can deliver the video signal to a remote monitoring facility, but only with severely degraded resolution and frame rate. Neither approach has been used to provide access to any available video source from several monitoring stations.
Another commonplace example is the still-image compression commonly used in digital cameras. These compression techniques may require several seconds to compress a captured image, but once done the image has been reduced to a manageably small size, suitable for storage on inexpensive digital media (e.g., floppy disk) or for convenient transmission over an inexpensive network connection (e.g. via the internet over a 28.8 kbit/sec modem).
Prior-art surveillance systems have been oriented towards centralized monitoring of the various cameras. While useful, this approach lacks the functional flexibility possible with more modern networking technologies.